HE [HAZRAT MAHDI (AS)] WILL DO EVERYTHING THAT THE MESSENGER OF ALLAH (SAAS) DID; HE [HAZRAT MAHDI (AS)] WILL DEMOLISH PREVIOUS FOUNDATIONS IN THE SAME WAY THAT THE MESSENGER OF ALLAH (SAAS) TORE DOWN THE FOUNDATIONS OF THE SYSTEM OF IGNORANCE, and he will restore Islam again from the beginning.
Mikyaal al-Makarem, Vol. 1, p. 5
When Hazrat Mahdi (as) appears he will intellectually vanquish all those atheist systems of the time that are built on denial, just as our Prophet (saas) did, and he will show people the invalidity of these systems’ infrastructure, teachings, philosophies, superstitions and beliefs. Following that, he will be instrumental in people living by the original essence of Islam – purged of all subsequent innovations and unrealistic practices – again as in the time of our Prophet (saas).